1. Field of the Invention
The invention relates to a compressor-wheel arrangement for turbochargers, in particular for exhaust-gas turbochargers, including a mounting/dismantling device and method.
2. Discussion of Background
Exhaust-gas turbochargers mainly comprise a casing having an integrated exhaust-gas turbine and a corresponding compressor, the exhaust-gas turbine and the compressor usually being arranged on a common shaft. An important precondition for the function of the exhaust-gas turbochargers is a rotationally locked shaft/hub connection on both the turbine side and the compressor side. Such a connection can be realized either in a frictional or positive-locking manner.
Frictional connections can be produced, for example, by pressing or shrinking the hub onto the shaft. However, such an operation requires a relatively large amount of work. In order to be able to take action in the interior of the turbochargers at an appropriate point in the event of both the repair and maintenance of the turbochargers, the latter must be largely dismantled and at the same time the shaft/hub connections must also frequently be released. However, this clearly increases the amount of effort required for maintenance and repair work. Therefore a considerably longer stoppage, i.e. withdrawal from service, of the internal combustion engine connected to the turbocharger can be expected.
U.S. Pat No. 5,193,989 discloses a positive-locking shaft/hub connection for the compressor wheel of a turbocharger. To this end, the compressor wheel has on the turbine side a fastening socket having a blind hole and an integrated internal thread which is screwed to the thread end of the turbocharger shaft. Formed in each case on both sides of the internal thread is a guide surface which corresponds with a corresponding guide surface of the thread end. In this solution, the zone of greatest stress concentration, which for every compressor wheel is located in the region of its greatest radial extent, is not weakened by a hole used for the fastening. Since the shaft/hub connection is therefore arranged outside the zone at risk, an especially robust fastening of the compressor wheel is achieved.
However, this advantageous fastening of the compressor wheel results in disadvantages during the mounting or dismantling. Since no access to the turbine side is possible in a turbocharger connected to an internal combustion engine, the requisite counter torque for detaching or fastening the compressor wheel cannot be applied. Consequently, the turbocharger components can neither be mounted nor dismantled from the compressor side. In order to maintain or repair it, the turbocharger, including the attached gas lines, must therefore be detached from the internal combustion engine. However, such a procedure requires a great deal of work and therefore leads to a longer withdrawal from service of the internal combustion engine connected to the turbocharger.
In contrast, a number of compressor-wheel arrangements for turbochargers are known (see, for example, DE-A1 43 30 380) in which the compressor wheel has a hub with a continuous bore. The turbocharger shaft reaching through the bore has a threaded end on which a nut serving to axially restrain the compressor wheel is guided. In these solutions, however, the shaft/hub connection is formed in the zone of greatest stress concentration. Widening of the hub bore and thus release of the shaft/hub connection may occur, in particular at high rotational speeds of the turbocharger. Accordingly, reliable fastening of the compressor wheel is not ensured in the long run.